Reproduction and Development of Flowering...

Chapter 24 Reproduction and Development

of Flowering Plants

Beekeeper: ©Liu Jin/AFP/Getty Images; honey bee: ©Stephen Dalton/Science Source

Copyright © McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.

Most Angiosperms Reproduce Sexually

Section 24.1

Flowers are the sex organs of angiosperms. This bee is gathering pollen that might deliver sperm to the next flower it visits.

Honey bee: ©Stephen Dalton/Science Source


Section 24.1

This ant is carrying a seed, which developed from a fertilized egg cell.

Ant: © Kris Mercer/Alamy/RF


Section 24.1

Flowers and seeds are produced by angiosperms that sexually reproduce, yielding genetically unique offspring

with traits derived from two parents.

Honey bee: ©Stephen Dalton/Science Source; ant: © Kris Mercer/Alamy/RF


Section 24.1 Figure 24.1

Some species of angiosperms also reproduce asexually, forming new individuals by mitotic division.

Aspens: © Steven P. Lynch/The McGraw-Hill Companies



Offspring produced asexually are genetically identical to each other and to their parents.




These aspen trees can reproduce either asexually, as suckers grow from roots, or sexually via seeds.




Similarly, the leaves of this kalanchoe plant produce genetically identical plantlets.

Kalanchoe: ©R Koenig/age fotostock



Asexual reproduction is advantageous when conditions are stable and plants are well-adapted to their surroundings.

Sexual reproduction produces variable offspring, increasing reproductive success in a changing world.

Aspens: ©Steven P. Lynch/The Mcgraw-Hill Companies; kalanchoe: ©R Koenig/age footstock;

honey bee: ©Stephen Dalton/Science Source; ant: © Kris Mercer/Alamy/RF

24.1 Mastering Concepts

When are sexual and asexual reproductioneach adaptive?


Angiosperm Sex: Flowers, Fruits, and Seeds

Section 24.2

The angiosperm life cycle is an alternation of generations with multicellular diploid and haploid stages.



The angiosperm life cycle is an alternation of generations with multicellular diploid and haploid stages.



This diagram is an overview of the angiosperm life cycle.

Let’s startwith theflower.



The first step in angiosperm reproduction is the formation of flowers on the mature sporophyte.

Section 24.2


A typical flower has four whorls of structures, all of which are modified leaves.

Figure 24.5

Section 24.2


The outer whorl is the calyx. It consists of sepals, which enclose and protect the inner floral parts.

Figure 24.5

Section 24.2


The second whorl is the corolla, which is made of petals.

Figure 24.5

Section 24.2


The third whorl is the male reproductive parts. Stamens are filaments with pollen-producing anthers on top.

Figure 24.5

Section 24.2


The fourth whorl is the female reproductive parts. A carpel includes:-the ovary, which encloses one or more ovules.-a stalklike style. The top of the style, called the stigma, receives pollen.

Figure 24.5


Section 24.2

Inside the flower, meiosis produces haploid spores that develop into gametophytes.



Anthers produce microspores, which divide into male gametophytes (pollen grains).

Ovules produce megaspores, which divide into female gametophytes (embryo sacs).

Pollen sacOvule

Megaspores (three degenerate)

Microspores

Ovule Polar nucleiEgg

Pollen grains



Some flowers release pollen grains in the wind.

Pollen: © Dr. Jeremy Burgess/Science Source



Other flowers attract animal pollinators, which unwittingly carry pollen between plants.

Hummingbird: © Corbis RF; butterfly: © MedioImages/Getty Images RF;

bat: © Merlin D. Tuttle/Bat Conservation International/Science Source



Often, the pollinator benefits from its association with plants—animals use plants for food, shelter, or a mating ground.

Hummingbird: © Corbis RF; butterfly: © MedioImages/Getty Images RF;

bat: © Merlin D. Tuttle/Bat Conservation International/Science Source

Clicker Question #1

An “imperfect” flower is one that lacks either male or female parts. A flower lacking male parts would still produce

A. pollen.B. anthers.C. an embryo sac.D. egg cells.E. Both an embryo sac and eggs cells are correct.

Flower: © Doug Sherman/Geofile/RF

Clicker Question #1

An “imperfect” flower is one that lacks either male or female parts. A flower lacking male parts would still produce

A. pollen.B. anthers.C. an embryo sac.D. egg cells.E. Both an embryo sac and egg cells are correct.




If a pollen grain lands on a receptive stigma, pollination occurs.

Ovule Polar nuclei

Egg

Pollen grains



When the pollen grain germinates, a pollen tube begins to grow toward the ovule.



Two sperm nuclei travel through the pollen tube to the ovule.


Section 24.2

The stage is now set for fertilization.



In double fertilization, these sperm nuclei fertilize the egg and the two polar nuclei.



Double fertilization results in a diploid zygote and triploid endospermnucleus.



After fertilization, the seed starts to develop.

A seed consists of an embryo, endosperm, and seed coat.

Seed coatEmbryoEndosperm



The zygote develops from a single cell into an embryo.



Cotyledons are the embryo’s “seed leaves.” Embryonic shoots and roots also form.



Endosperm cells divide rapidly and nourish the embryo.

Cord seed: © John D. Cunningham/Visuals Unlimited; shepherds purse: © Steven P. Lynch/The McGraw-Hill Companies



The seed coat is a tough outer layer that protects the embryo from damage, dehydration, and predators.

Cord seed: © John D. Cunningham/Visuals Unlimited; shepherds purse: © Steven P. Lynch/The McGraw-Hill Companies



At the same time, a fruit develops from the ovary enclosing the developing seed(s).

Seed coatEmbryoEndosperm



These photos show how the fruit forms.After pollination, the flower loses its petals.

Photos: © Brent Seabrook

Section 24.2


A developing seed releases hormones that trigger fruit formation. The ovary swells.

Photos: © Brent Seabrook Figure 24.10

Clicker Question #2

Angiosperms and humans reproduce sexually. Pollination in plants is analogous to ___ in humans; seed development in plants is analogous to ___ in humans.

A. sexual intercourse; growth of the fetusB. dating; going through pubertyC. fertilization; early childhoodD. gamete formation; birthE. None of the choices is correct.


Section 24.2 Table 24.1


Fruits come in many forms.

Cherry and pineapple: © Ingram Publishing/Alamy RF; strawberry: © Corbis RF



Fruits protect and disperse seeds. Seeds carried away from parent plants decrease the

chance of competition among parents, offspring, and siblings.

Bird: © Rod Planck/Science Source; dog:© Scott Camazine/Science Source; dandelion: © Adam Hart-Davis/Science Source

Section 24.2


Unripe fruits, which contain immature seeds, are usually distasteful. Ripe fruits are tasty; mature seeds are deposited

in droppings.

Bird: © Rod Planck/Science Source; dog:© Scott Camazine/Science Source; dandelion: © Adam Hart-Davis/Science Source Figure 24.11

Section 24.2


Prickly fruits stick to feathers or fur.


Section 24.2


Some fruits catch the wind with tufts of fluff. Still others float in water currents.



How does pollen move from one flower to another, and why is this process essential for sexual reproduction?


Section 24.2

How does the embryo continue developing into a mature sporophyte?

Plant Growth Begins With Seed Germination

Section 24.3


Continued development requires seed germination, the resumption of growth and development after a period of seed dormancy.

Germination requires water, O2, and a favorable temperature.

Sprout: © Corbis RF

Section 24.3


The seed absorbs water and swells, rupturing the seed coat and exposing the embryo to O2.


Section 24.3


Meanwhile, enzymes break down the endosperm’s starch into sugars.

The availability of O2 and sugars means cellular respiration can resume in the embryo. Cell division at apical meristems rapidly lengthens the young roots and shoot.


Section 24.3


At first, the only energy source is fuel stored in the endosperm.


Section 24.3


After the shoot emerges from the ground and the first leaves unfold, photosynthesis begins.


Section 24.3


Monocots and eudicots, two groups of plants, have slightly different development patterns.

Figure 24.12

Monocot development Eudicot development

Corn sprout: ©Dwight Kuhn; bean sprout: ©Ed Reschke

Angiosperm Anatomy

Angiosperm Categories

Angiosperms(flowering plants)are divided into twotypes: Monocots and Dicots

They differ basedon a number ofcharacteristics

Monocot Dicot

Monocot and Dicot Characteristics

Tissues of the Plant

Dermal tissue: Analogous to our skin

Vascular tissue: Vaguely like acirculatory system

Ground tissue: Support tissue

Dermal Tissue System

Function:Protection from the environment and water loss

Tissues:Epidermis - outermost single layer off cells on herbaceous plant parts. May be covered by waxy cuticleBark - a corky tissue that replaces epidermis on woody plant parts

Vascular Tissue System

Function:Translocation of water, nutrients, sugars and hormones throughout the plant

Tissues:Xylem - conducts water and nutrients up roots to stems and leavesPhloem - conducts water, sugar, hormones, etc. down to roots

Ground Tissue System

Function:Storage, support, filler tissue and site of some photosynthesis.

Plant Structure

•Seed and Seedling Structure•Growth Tissues (Meristems)•Root Structure•Stem Structure•Leaf Structure•Flower Structure

Seed Structure

Seed StructureSeed coat or testa protects the seed from the environmentCotyledons contain the endosperm, a nutritive tissue that accumulates starch, protein, and fats to provide for the growth of the embryoEpicotyl in most plants develop into the leavesHypocotyl develops into the stemRadicle first to emerge from the seed and develops into the root

Seedling Parts

Meristem (Growth Tissue)

Plants grow from localized areas called meristems.

They are discrete regions or groups of cells that have the ability to continue cell division for the life of the plant.

Meristem Location

Stem Functions

Functions:Anchorage: secures plant to ground or for epiphytes to branchesAbsorption: water and nutrients from soilStorage: ex.. sweet potato, carrot, etc.Propagation: ex. dahlia or sweet potato tuberous roots, blackberry

Stems and the Vascular System

Xylem cells are dead, they carry water and dissolved nutrients from the roots to the leaves.Phloem cells are living, they conduct food from the leaves to the roots.

Dicot Stem Monocot Stem

Stem FunctionsBud - an un-elongated stem containing primordial leaves and/or flowersTerminal bud - a bud at the tip off a stemAxillary or Latteral bud - buds along the side off a stem that grow out to form a side branchesFlower bud - a bud that develops into flowers; usually larger than vegetative budsLeaf scar - marks the former attachment point off a leaf or petiole to the stemNode - part off stem where leaves, flowers, fruits, buds and other stems are attached

Leaf FunctionsPhotosynthesis: it mainly occurs in leavesRegulate water loss: by opening and closing guard cellsStorage: ex. carbohydrates & water in chivesSupport: ex. tendrils on grapeProtection: ex. spines on cactiAttraction: ex. bracts on poinsettiaPropagation: ex. piggyback plant with plantlets on leaves

Leaf Interior

Leaf Arrangement

Alternate - one leaf attached per node, usually staggered (spiral) along stem.Opposite - two leaves (a pair) attached per node, usually opposite each other.Whorled - three or more leaves attached per node, usually equally

spaced around the node.

Simple and Compound Leaves

Simple Leaf Compound Leaf

Flower Structure

or Corolla or Calyx

Receptacle – swollen end of stem that supports flowerSepal – protective parts around flower budPetal –Colorful parts to attract pollinatorsStamen – male part of flower

- Anther produces pollen- Filament elevates anther

Carpel – female part of flower- Stigma – end that receives pollen- Style – elevates stigma- Ovary – contains ovules (eggs)

Monocot Vs. Dicot Plants

Root Diversity

Taproot (m) Fibrous root system(d)

Clicker Question #3

A seed that lands on dry pavement is unlikely to germinate because it does not receive enough

A. light.B. oxygen.C. food.D. water.



What are the events of early seedling development?


Section 24.4

Hormones Regulate Plant Growth

Chemicals called hormones travel between cells and regulate many aspects of plant growth.

Figure 24.14Apical dominance: © Nigel Cattlin/Visuals Unlimited

Section 24.4


Five hormones cue many of the major changes in plant growth and development:• Auxins• Cytokinins• Gibberellins• Ethylene• Abscisic acid


Section 24.4


Auxins stimulate fruit development, control elongation of cells in a stem, and suppress growth of lateral buds.


Section 24.4


Cytokinins stimulate cell division in many plant parts, delay shedding of leaves, and stimulate growth of lateral buds.


Section 24.4


Auxins are primarily released from the shoot tip, and cytokinins are primarily released from the roots.The counteracting effect of these hormones is called apical dominance.


Section 24.4


If the shoot tip is in place, auxins suppress the growth of lateral buds.

Figure 24.14

Apical dominance

Apical dominance: © Nigel Cattlin/Visuals Unlimited

Section 24.4


Removing the shoot tip reduces the auxin concentration. Cytokinins stimulate cell division in lateral buds.

The plant’s growth becomes bushier.

Figure 24.14

Apical dominance

Apical dominance: © Nigel Cattlin/Visuals Unlimited

Section 24.4


Gibberellins also stimulate shoot elongation. Farmers use these hormones to stimulate stem elongation and fruit growth.

Figure 24.15Grapes: © Sylvan Wittwer/Visuals Unlimited

Section 24.4


Ethylene hastens fruit ripening and stimulates shedding of leaves, flowers, and fruits.

Figure 24.APhoto: © David G. Clark

Section 24.4


Ethylene caused the flowers on the left to wither. The flowers on the right are genetically engineered to have mutant ethylene receptor genes.

Figure 24.APhoto: © David G. Clark

Section 24.4


Abscisic acid inhibits shoot growth, maintains seed dormancy, and stimulates closure of stomata and shedding of plant parts.

Tree: © Ingram Publishing/RF

Section 24.4


This figure summarizes how hormones affect plant germination and development.

Figure 24.30

Clicker Question #4

Researchers first discovered gibberellins in diseased rice plants. A gibberellin-producing fungus infected the plants, causing abnormal growth. How do you think the researchers could identify the infected plants in the field?

A. The plants were abnormally short.B. The plants were abnormally tall.C. The plants shed their leaves.



List the major classes of plant hormones and name some of their functions.


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